I've been light poisoning my babes, how bad is this?

[pompeii]

Well I have about a week or tow left of flowing and the majority of my leaves are pale yellow and everyday a handful die. I am pretty sure the problem is light poisoning. I have a 600w light in less a 3x3 (little less than 3x3 actually) and the light is hovering about 7 inches away from the plants. Needless to say the buds are fat, dense, and encrusted with THC glands but I am certain the plants are getting light poisoning from the amount of pale yellow / dying leaves.

So my question is how bad is light poisoning for the plants? How much does it affect yield? This is my first grow so I don't have other grows to compare it to, next time I will certainly back off on the light.

 

[Syndicate]

For reference light poisoning I believe refers to abnormal lighting schedule during flower, done or purpose or accidently, sometimes resulting in sex reversal.

I think what you mean is more like light bleaching @66 watts a square I've seen it but it is usually limited to the parts of the plant closest to the bulb.If thats all it is it's usually only a cosmetic problem, hard to tell though from only a description.

 

[pompeii]

Thanks for the clarification syndicate.

 

[TokeItUp420]

If you only have a week or two left, then it sounds pretty normal. Have you been cutting back on nutrients? Most growers will cut back on nitrogen late in flower so it doesn't smoke as harsh. When this happens, the leaves will start to yellow and some may drop.

I guess I should have asked, is the pale yellowing just at the top of the plant where the light would be hitting the plant strongest? Or is it kinda all over or more towards the bottom? Without pics it is hard to give you an informative answer to your question. Good luck!


Peace...
Toke

 

[pompeii]

I stopped giving them nitrogen like 4 weeks ago. I flushed 2 of them on sunday and the other 1 about a week and a half ago. They are looking very sick / dying except those glorious sticky buds

The pale / yellowing is definitely occuring towards the top, and of the 3, one plant doesn't have too much yellowing going. It's the only plants that is less exposed to the light, this is why I believe it's light bleaching.

Sorry for lack of pics

 

[Space Ghost]

you're fine

 

[Whatever]

You won't get bleaching with a 600 7" away...you need to be more like 6". I know it does not sound like much but that's what I've been told. I ran 1000 MH's 9" from the tops and no bleaching and that was right at the threshold. I was expecting something right at the very top of the tops but nothing. For 600's I like to keep 600's about 18" away from the tops when running HPS though. I've heard people talk about sodium poisoning when keeping an HPS too close but never saw much of it with anyone. I know getting an HPS too close can cause bolting. I bet those tops might be a bit warm though and that can cause some actual burning if you're air cooling is not up to snuff.

At this stage it kind of just sounds like they're just finishing up. What medium are you in? I've had stuff in soil that turned yellow prematurely cause my pH slowly dropped until it was very low, then locking some nutes out so the plants kind of died on the vine.

 

[pompeii]

I am using soil, and would add some natural PH up once every 3 feedings.

 

[Whatever]

Do you know what the pH of the soil is? It should be no lower than 5.8. I usually like to see the pH drop toward 6 as flowering progresses cause that's a more happy zone for fungi which are greatly responsible for phosphorous processing/transport. Fungi like a lower pH while bacteria like it a bit higher. Once pH starts to drop below 5.8ish it will tend to crash as the soil becomes fungal dominant and they naturally drive pH down...something like that. When I first started with soil the pH dropped down to around 4.5 in some pots and the plants looked pretty shitty...lol.

The best bang for the buck soil pH meter I've found is the one shown below made by Control Wizard. I got mine for $60 + shipping. A friend tested his against a $400 soil meter and the Control Wizard was basically spot on.